The present application relates to an electrolyte containing an organic acid and a sulfone compound, and a secondary battery using the electrolyte.
In recent years, portable electronic devices such as video cameras, digital still cameras, cellular phones, and notebook computers have become increasingly popular. There is strong demand for reducing their size and weight and extending their lifetime. Under such trends, development of batteries, in particular, secondary batteries, that can be used as power sources, are small and light-weight, and achieve high energy densities is proceeding.
In particular, lithium-ion secondary batteries that utilize occlusion and release of lithium ions and lithium metal secondary batteries that utilize precipitation and dissolution of lithium metal for charge/discharge reactions are considered to have great potentials. This is because they achieve energy densities higher than that achieved by lead batteries or nickel-cadmium batteries.
A secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode collector and a positive electrode active material layer on the positive electrode collector. The negative electrode includes a negative electrode collector and a negative electrode active material layer on the negative electrode collector. The electrolyte contains a solvent and an electrolyte salt.
The electrolyte functions as a medium for charge/discharge reactions and greatly affects the performance of secondary batteries. Thus, various investigations have been conducted on the composition of the electrolyte.
In particular, in order to improve cycle characteristics and the like, formic acid, acetic acid, oxalic acid, malonic acid, maleic acid, fumaric acid, benzoic acid, and the like are used (e.g., refer to Japanese Unexamined Patent Application Publication Nos. 2000-012079 and 2006-351242). Note that oxalic acid, succinic acid, malonic acid, adipic acid, sebacic acid, and phosphoric acid and their metal salts are also used in positive and negative electrodes as well as the electrolyte (e.g., refer to Japanese Unexamined Patent Application Publication Nos. 09-190819, 09-190820, 2004-335379, 2005-011594, and 2006-134684). In order to improve cycle characteristics, storage characteristics, and the like, disulfonic anhydrides, sulfonic-carboxylic anhydrides, etc., are used (e.g., refer to Japanese Unexamined Patent Application Publication Nos. 2004-022336 and 2002-008718).